Chronic Ventilatory Failure

Question 1

What parameters is Chronic Ventilatory failure marked by in an arterial blood gas?

Answer 1

The same as type 2 respiratory failure:
PaO2 <8kPa
PaCO2 >6.0kPa
Normal blood pH
Elevated bicarbonate levels (HCO3-)

Question 2

Chronic vs acute

Answer 2

Chrnic has a normal pH level becuase the body has had time to adapt and the kidneys have retained bicarbonate (week buffer) so the pH has gone back to normal (7.4). In acute, the pH is higher as the levels of CO2 have risen and there ahs not been time to equilibrilate.

Question 3

pH proportional to ?

Answer 3

[HCO3-]/[ppCO2]

Question 4

How is blood pH maintained in Chronic Ventilatory failure(Chronic Type 2 vrespiratory failure)?

Answer 4

Body retains week bicarbonate buffer from the kidneys HCO3-

Question 5

Chronic Ventilatory failure includes: (give examples of)
Airways disease
Chest wall abnormalities
Respiratory muscle weakness
Central Hypoventilation

Answer 5

Airways disease: COPD (mainly severe or obese + moderate), bronchiectasis

Chest wall abnormalities: Kyphosis (inefficient ventilation - fatigue - impaired ventilation)

Respiratory muscle weakness: (Notably diaphragm, intercostal /accessory muscles) Motor Neurone disease (ALS) death often from Chronic Vent failure , Muscular dystrophy, Glycogen Storage Disease (Pompe’s disease)

Central Hypoventilation: Obesity Hypoventilation Syndrome - linked to sleep Apnoea, get abnormailites during sleep first, then progresses into daytime, Congenital Central Hypoventilation Syndrome (Ondine’s curse) - newborns with vent failure,

Question 6

Symnptoms

Answer 6

Breathlessness
Orthopnoea Breathless ness when lying flat (due to no gravity to help weak diaphragm)
Ankle swelling (Cor Pulmonarle - low po2, hypoxic vasoconstriction, right side heart failure, extra pressure in veins, swelling at ankles)
Morning Headache - excess CO2 in blood acts as vasodilator in brain - headaches
Recurrent chest infections
disturbed sleep

Question 7

Examination findings? What is Paradoxical abdominal wall movement?

Answer 7

Reflects underlying disease
ankle oedema
abdominal wall movement - when lying, instead of abdo wall going up and up, does the opposite due to weak/dysfunctioning diaphragm

Question 8

Investigations - neuromuscular disease suspect:

Answer 8

Looking specifically fo rmuscle weakness: Lung function tests, Hypoventilation tests, potential Fluroscopic screening of diaphragms.

Question 9

During REM sleep, which muscles are activated/deactivated?

Answer 9

Only the diaphragm is activated

Question 10

How do you test Lung Function when looking for muscle damage

Answer 10

Vital capacity whilst standing and lying

Mouth and SNIP (nose) pressures, how much pressure against resistance able to expire/inspire

Question 11

How do you assess Hypoventilation?

Answer 11

Hypoventilation usually occurs in sleep first (during REM sleep only the diaphragm is activated so if there is a weakness there then it is amplified!) so:

Early morning ABG - reflect physiology during sleep
Overnight oximetry
transcutaneous CO2 monitoring - closely reflects CO2 in blood

Question 12

If we think diaphragm is weak, what test?

Answer 12

Fluoroscopic screening of the diaphragms - looks at movements of diaphragm

Question 13

Pulmonary Function spirometry results with marked neuromuscular weakness, reflective of what type of respiratory pattern?

Answer 13

restrictive

Question 14

Treatment

Answer 14

Not curable unless underlying condition is.

But treatable with:
Domiciliary non invasive ventilation (NIV)
supplementary oxygen therapy
if v bad then tracheal ventilation (trachetomized ventilation)